Various methods have been employed to obtain high burning rate propellants. The method selected has to be suited for the type propellant, burning time required, and motor design.
The prior art use of liquid burning rate catalysts (particularly of the organoiron or carborane types) has resulted in problems associated with the use of such catalysts because of their relatively high volatility, their high freezing points, and their tendencies to migrate within the propellant and into the liner and insulation of the rocket. In order to overcome these migratory tendencies, it has been necessary (in one technique to overcome the migratory tendencies) to incorporate high percentages of burning rate promoter into the insulation to produce a near-equilibrium situation insofar as catalyst migration is concerned, thus further complicating the manufacture of these types of solid rocket motors. This technique to hinder catalyst migration did not prove to be a solution to catalyst migration.
Other approaches have been made toward solving the problems associated with catalyst migration, particularly in several propellants under active development which contain appreciable amounts of liquid burning rate additives such as those of the ferrocene and carborane type. These additives which have been determined to be extremely mobile will migrate into the liner, insulation, or motor case (if the case is of the composite-fiber/resin type), and as a result of additive migration, ballistic anomalies or catastrophies have often resulted.
Carborane type propellants containing carboranyl methyl ethyl sulfide (CMES), carboranyl methyl propyl sulfide (CMPS), mixtures of CMES/CMPS, normal hexylcarborane (NHC), and carboranyl methyl proprionate (CMP) bond well to metal motor cases that have been grit blasted and degreased. Thus, their use in this combination does not relate to the additional problems associated with penetration of case and/or liner materials by a carboranyl catalyst.
Carborane propellants of the types described above are of particular interest for use in composite motor cases (glass fiber/epoxy resin or graphite/epoxy resin) under high lateral and axial loading conditions; i.e., conditions that require excellent bond strength between the propellant/liner/insulation/case system. The migration of catalyst problem associated with carborane propellants used in composite motor cases has been lessened by a partially satisfactory propellant/liner/case bond system by using aluminum foil bonded to the propellant on one side and to a liner on the other side. The technique was earlier used in combination with a metal case, and the liner and propellant with aluminum foil between the liner and propellant is bonded to the metal case. The problem associated with the aluminum foil technique which was used on the joint US-Canada Metrocket Program include "pinholes" in the foil and cracking/tearing of the foil if the grain exterior geometry is complicated.
Advantageous would be a combination which can utilize the good bonding characteristic of propellants of the carborane type to bare metal and eliminate the problems encountered with foil.
Therefore an object of this invention is to provide a method of bonding propellants containing carborane, ferrocene, or nitroglycerin to a metal barrier to prevent migration into the liner, insulation, or composite motor case.
Another object of this invention is to provide a method of bonding propellants containing carborane, ferrocene, or nitroglycerin to a metal barrier to prevent migration into the liner, insulation, or composite motor case having complex case geometries.